LASUS, Greek lyric poet, of Hermione in Argolis, flourished about 510 B.C. A member of the literary and artistic circle of the Peisistratidae, he was an instructor of Pindar in music and poetry and the rival of Simonides. The dithyramb (of which he was sometimes considered the actual inventor) was developed by him, by the various changes in music and rhythm, into an artistically constructed choral song, with an accompaniment of several flutes. It became more artificial and mimetic in character, and its range of subjects was no longer confined to the adventures of Dionysus. Lasus further increased its popularity by introducing prize contests for the best poem of the kind. His over-refinement is shown by his avoidance of the letter sigma (on account of its hissing sound) in several of his poems, of one of which (a hymn to Demeter of Hermione) a few lines have been preserved in Athenaeus (xiv. 624 E). Lasus was also the author of the first theoretical treatise on music.